1. Field of the Invention
The present invention relates to an image forming apparatus such as a copying machine, a printer and a facsimile and a developing device used in these apparatuses.
2. Description of the Related Art
In a conventional developing device, a developing sleeve is rotatably supported at both longitudinal ends. Therefore, when the developing sleeve is deflected, S-D gap (a distance between the developing sleeve and a photosensitive drum) in the longitudinal center of the developing sleeve becomes wider. Thus, the image density at end portions in the longitudinal direction of the photosensitive drum is sometimes lowered.
In Japanese Patent Laid-Open No. 2010-139922, the depth of the concave portion of an uneven shape of the developing sleeve is deepened more as it nears both ends in the longitudinal direction. Thus, an amount of toner carried on both longitudinal end portions is increased, thereby suppressing a decrease in image density at both end portions in the longitudinal direction.
However, in the developing device using a two-component developing system, a developer regulating member is provided in a position close to the cut-pole of the magnet roll (magnetic member) in the photosensitive drum. The developer regulating member is often a plate-shaped blade. In addition, the developer regulating member is not firmly supported because of saving space and saving number of parts, thereby the deflection is more likely to occur. Accordingly, a simple developer regulating member with a magnetic material is attracted to the cut-pole.
Because the developer regulating member becomes closer to the development sleeve as it becomes farther from the supporting portion, S-B-gap (a distance between the developing sleeve and the developer regulating member) is narrowed at the position far from the supporting portion. Thus, M/S (developer weight per unit area) in the longitudinal center of the developer sleeve (developer bearing member) is lowered and the amount of toner which can be developed on the photosensitive drum is lowered.